The present invention relates to an electrophotosensitive material. More particularly the invention relates to the electrophotosensitive materials ideally utilized for the image forming apparatus such as copying machine.
Recently, an organic photosensitive materials are utilized for the electrophotosensitive material because the organic layer have wide freedom for the functional designing as well as workability and advantageous in production costs. It is well known that as the organic photosensitive material, the high sensitive functional types electrophotosensitive material provides a photosensitive layer wherein the electric charge generating with exposure to light function with a charge-generating material and the electric charge-transferring function with a charge-transferring material which materials are separated type.
There are variety of function-separated type photosensitive material such as multilayer type which comprises a charge-generating layer at least containing a charge-generating material, and a charge-transferring layer at least containing a charge-transferring material and a binding resin; and single layer type photosensitive material wherein both of a charge-generating material and a charge-transferring material are dispersed into a binding resin.
The multilayer type photosensitive material is different from the single layer type, have an advantage in providing a high sensitivity and wide availability for selecting photosensitive material because the functions thereof are separated into two.
For reasons that major charge-transferring materials are positive charge, and that durability is given to the surface, the structure of multilayer type photosensitive material for negative electrification wherein the charge-generating layer is provided on the conductive substrate, and the charge-transferring layer is provided thereon, is generally employed. However, the multilayer type photosensitive material for negative electrification may generate ozone into the ambient atmosphere on negative electrifying, causing the sensitive layer to deteriorate and copying environment to contaminate, and the positive charge toner, which is difficult to make, is necessary in developing process.
On the other side, the above mentioned single-layer type electrophotosensitive material can be charged negatively. Accordingly, the single-layer type electrophotosensitive material can be used with negative charge toner which is easy to manufacture. The negative charge toner may be produced with various materials. However, both of electron and positive hole are moved in one layer wherein either electron or positive hole are trapped, causing the residual potential increasing. Moreover, it is yet a problem that electrophotosensitive characteristics such as the electrification characteristics. sensitivity and residual potential much depend upon the combination of charge-generating material and charge-transferring material.
In order to remove the above mentioned problems, the electrophotosensitive material in which diamine derivatives are used as charge-transferring material, is proposed. The diamine derivatives are not only having symmetrical molecular structure, taking no part in isomerization reaction caused by light irradiation and providing light stability but features showing large drift mobility and low electric field strength dependency.
The electrophotosensitive material using diamine derivatives as charge-transferring material have high sensitivity and low residual potential.
However, these electrophotosensitive material are not yet complete to obtain the sufficient sensitivity and stability of surface potential in repetition of copying process.